1. Preheat the oven to 350°, then peel and slice sweet potatoes. I sliced mine using a mandoline, but a knife works great as well. The mandoline speeds up the process significantly and gives you even slices. Coat a pie dish with cooking spray, then fill the bottom of the dish with a layer of sweet potato slices. Cut the sweet potato rounds in half and fill around the edges of the pie dish; round side facing up. Once the entire dish is filled, coat one more time with cooking spray. Bake for 20 minutes. Turn heat up to 375°.